Liquid jet apparatuses include, for example, an ink-jet recording apparatus equipped with an ink-jet recording head including a plurality of pressure generating chambers which generate pressure for ejecting ink droplets using piezoelectric elements or heater elements, a common reservoir which supplies the pressure generating chambers with ink, and nozzle orifices communicating with the respective pressure generating chambers. In the ink-jet recording apparatus, ejecting energy is applied to ink in the pressure generating chambers communicating with nozzles corresponding to print signals, thus ejecting ink droplets from the nozzle orifices.
Such ink-jet recording heads are broadly classified into two types regarding the pressure generating chambers, as described above: one in which heater elements such as resistance wires for generating Joule heat in accordance with drive signals are provided in pressure generating chambers, and ink droplets are ejected from nozzle orifices by bubbles generated by the heater elements; and one of a piezoelectric vibration type in which part of pressure generating chambers are constituted of a vibration plate, and ink droplets are ejected from nozzle orifices by deforming the vibration plate by using piezoelectric elements.
Moreover, for the ink-jet recording head of the piezoelectric vibration type, two types are put to practical use: one which uses a piezoelectric actuator of a longitudinal vibration mode that extends and contracts in the axial direction of the piezoelectric elements; and one which uses a piezoelectric actuator of a flexure vibration mode.
In the former, the capacities of the pressure generating chambers can be changed by bringing end faces of the piezoelectric elements into contact with the vibration plate, and therefore a head suitable for high-density printing can be fabricated. However, there is a problem that a manufacturing process is complex as follows: this type requires a difficult process of cutting a piezoelectric element into a comb-teeth shape while allowing the piezoelectric element to coincide with the array pitch of the nozzle orifices, and work of positioning and fixing the cut piezoelectric elements to the pressure generating chambers.
On the other hand, in the latter, the piezoelectric elements can be made and fixed to the vibration plate by a relatively easy process in which a green sheet of piezoelectric material is attached to the vibration plate in accordance with the shapes of the pressure generating chambers and then baked. However, because of the utilization of flexure vibration, a certain area is required, and therefore there is a problem that high-density arrangement is difficult.
Meanwhile, in order to eliminate the disadvantage of the latter recording head, for example, as disclosed in Japanese Unexamined Patent Publication No. Hei 5(1993)-286131, a recording head has been proposed, in which a uniform piezoelectric material layer is formed over the entire surface of a vibration plate by deposition technology, and the piezoelectric material layer is cut into shapes corresponding to pressure generating chambers by lithography, thus forming piezoelectric elements independently for the respective pressure generating chambers.
This eliminates work of attaching the piezoelectric elements to the vibration plate, and the piezoelectric elements can be made and fixed thereto at high density by a precise and simple method, namely, lithography. In addition, there is an advantage that the thickness of the piezoelectric elements can be reduced and therefore high-speed drive becomes possible.
In general, in such a conventional ink-jet recording head, ink cavities (pressure generating chambers) are formed in a silicon substrate, and a vibration plate constituting one surfaces of the ink cavities is formed of a silicon oxide film. Accordingly, if alkaline ink is used, the silicon substrate is gradually dissolved by the ink, and the width of each pressure generating chamber changes with a lapse of time. This causes changes in pressure to be given to the pressure generating chambers by the drive of piezoelectric elements, and therefore there is a problem that ink ejecting characteristics are gradually deteriorated. In order to solve such a problem, for example, as disclosed in Japanese Unexamined Patent Publication No. Hei 10(1998)-264383, there is a recording head in which a silicon substrate and the like are prevented from being dissolved by ink by providing a hydrophilic and alkaline-resistant film, e.g., a nickel film or the like, in ink cavities.
As described above, it is possible to prevent the dissolution caused by ink to a certain degree by providing the nickel film or the like in the ink cavities. However, since the nickel film or the like is also gradually dissolved by ink, there is a problem that ink ejecting characteristics are degraded after a long period of use. In particular, when ink at a relatively high pH is used, the rate of solution is increased, and therefore ink ejecting characteristics are also degraded within a relatively short period.
Moreover, for example, as disclosed in Japanese Unexamined Patent Publication No. 2002-160366, there is a structure in which the destruction of piezoelectric elements due to an external environment is prevented by joining a sealing plate having a piezoelectric element holding portion for sealing the piezoelectric elements onto one surface, on a piezoelectric element side, of a passage-forming substrate in which pressure generating chambers are formed. In such a sealing plate, a reservoir portion constituting part of an ink chamber common to the pressure generating chambers is provided, but in reality the resistance to ink in the reservoir portion is not taken into consideration. In other words, the reservoir portion is a portion where ink to be supplied to the pressure generating chambers is held in reserve and hardly becomes a direct factor in the degradation of ink ejecting characteristics. Therefore, in a conventional ink-jet recording head, the resistance to ink in the reservoir portion has not been taken into consideration.
However, for example, if alkaline ink is used in the case where a single crystal silicon (Si) substrate is used as a material for a sealing plate, the inner wall surface of a reservoir portion are gradually dissolved by the ink similarly to the case of pressure generating chambers. When the shape of the reservoir portion is greatly changed accordingly, a defect in the supply of ink to pressure generating chambers is caused and may lead to the degradation of ink ejecting characteristics.
Further, there may be cases where dissolved materials of the sealing plate generated from the inner wall surface of the reservoir portion dissolved in ink become deposits (Si) separated in the ink along with, for example, a temperature change or the like. The deposits are carried with the ink to the pressure generating chambers, and so-called nozzle blockage may be also caused.
Note that the above-described problems exist not only in an ink-jet recording head for ejecting ink but also similarly exist in other liquid jet head for jetting alkaline liquid other than ink, as a matter of course.